1. Field of the Invention
The present invention relates to a refrigeration cycle using a six-way change-over valve, and particularly to a refrigeration cycle using a six-way change-over valve in which refrigerant can flow through indoor and outdoor heat exchangers in a fixed direction at any time.
2. Description of Related Art
A refrigerant circuit for use in a conventional air conditioner includes a compressor, a four-way change-over valve, a heat exchanger at an using side, an expansion device, a heat exchanger at a heat source side, etc. When a heating operation is carried out, refrigerant flows through the above elements in this order. On the other hand, when a cooling operation is carried out, the refrigerant flows through the above elements in the opposite direction to the above direction by switching the four-way change-over valve. Recently, an air conditioner using refrigerant (HFC type refrigerant) or substitute refrigerant such as non-azeotropic mixture refrigerant formed of refrigerant having high boiling point and refrigerant having low boiling point or the like, has been developed.
In the air condition using the non-azeotropic mixture refrigerant, the refrigerant having low boiling point is evaporated prior to evaporation of the refrigerant having high boiling point. Therefore, when the heat exchanger serves as an evaporator, temperature difference occurs between refrigerant inlet and outlet sides of a heat exchanger, so that the temperature at the inlet side of the heat exchanger becomes lower than that at the outlet side of the heat exchanger. On the other hand, when the heat exchanger serves as a condenser, the refrigerant having high boiling point is condensed prior to condensation of the refrigerant having low boiling temperature. Therefore, the temperature at the inlet side of the heat exchanger becomes higher than the temperature at the outlet side of the heat exchanger. Accordingly, when such non-azeotropic refrigerant is used in an air conditioner, it is efficiently preferable to design the refrigerant circuit so that the refrigerant and the air (or water) are forced to flow in opposite directions, that is, it is preferable to establish a counterflow relationship between the refrigerant flow and the air flow.
In general, refrigerant pipes are disposed in a multiple arrangement in the heat exchanger. That is, the refrigerant first flows through a pipe on the front face of the heat exchanger and then turns to and flows through a pipe on the back face thereof. Alternatively, the refrigerant first flows through a pipe on the back face of the heat exchanger and then turns to and flows through a pipe on the front face thereof. Accordingly, in order to improve the efficiency of the heat exchanger, the priority of the face of the heat exchanger on which the refrigerant first flows must be determined on the basis of the disposing position of the fan (i.e., the front face of the heat exchanger or the back face of the heat exchanger). The improvement of the efficiency as described above is applied to both cases where the refrigerant comprises HFC type refrigerant and where it comprises non-azeotropic mixture refrigerant.
However, when one of the heating operation and the cooling operation is selectively performed by switching the four-way change-over valve as described above, the refrigerant and the air (or water) necessarily flow in the same direction (in parallel to each other) either in the heating operation or in the cooling operation because the refrigerant flow direction in each of the heat exchanger at the user side and the heat exchanger at the heat source side is completely reversed between the heating operation and the cooling operation. Therefore, this conventional air conditioner has a problem that a coefficient of performance (COP) is reduced.